What Causes Bruise On Lower Spine?

I'm 16 I weigh 120 lbs. And am 5'6" I had a 5 cm. On my left ovary and now I have 2 minor ones on my right. I have been having back pains with neck pains for 3 weeks now and just noticed a 4-5 inch bruise on my lower spine that has not been hit or smacked. I'm scared because I have been told it could a serious spinal issue.